Age-related macular degeneration (ARMD) is the leading cause of blindness among persons over fifty in the United States and other countries. Two forms of age-related macular degeneration are known: (1) neovascular, also known as exudative, age-related macular degeneration (E-ARMD) and (2) nonneovascular, also known as nonexudative, age-related macular degeneration (NE-ARMD). NE-ARMD is characterized by the presence of drusen, yellow-white lesions of the retinal pigment epithelium within the macula, and by other abnormalities of the retinal pigment epithelium, including retinal cell death.
Although the exact etiology of ARMD is not known, several risk factors seem to be important for the manifestation of this disease. For example, ARMD may be caused by chronic exposure of the retina to light. The presence or absence of certain nutrients in the diet, such as the antioxidant vitamins E and C, also may affect one's predisposition for ARMD. Other conditions, such as hypertension and smoking, are also considered to be important risk factors for the development of this disease.
Several therapeutic methods have been tried. For example, vitamins and dietary supplements have been used for the purpose of delaying the onset of disease. Thalidomide is being investigated to determine if it will slow down or arrest new vessel formation. Laser or radiation has been used to destroy new vessels. However, none of these methods has led to successful results and no definitive treatment for ARMD has been developed to date.
Additionally, retinal translocation has been used to change the position of the fovea. Retinal translocation is a surgical method that involves injecting a fluid, such as saline solution, under the retina to loosen the retina. Gas is then injected into the vitreous to reattach the retina, and a scleral indentation is formed. This procedure results in displacement of the retina inferiority, placing the fovea on normal retinal epithelium.
However, the retinal displacement is generally unpredictable and minimal. For example, the displacement is generally only about 500–1000 microns. Thus, there is little area for subsequent coagulation of the subretinal membrane. Additionally, the displacement does not occur immediately during surgery, but during a recovery process that generally lasts about 24 hours. The displacement occurs due to the position of the head of the patient in a recovery situation. For example, since the head is generally held in an upright manner, the gas injected into the eye rises, thus forcing the retina from the top, moving the retina inferiority with respect to its original position. Furthermore, the retina can generally only be easily moved inferiority since the gas rises up relative to the eye and can only exert pressure to move the retina down.
Additional retinal translocation procedures exist wherein the retina is literally cut 360° and disassembled for translocation relative to the underlying tissue prior to re-assembly of the retina after its rotation. This procedure has 15–30% rate of severe complication and loss of vision.
These procedures are intended to treat conditions wherein the tissue underlying the macular (central vision) portion of the retina becomes diseased. Degenerative conditions of this sort may result in the photoreceptors of the macula portion of the retina adjacent to the underlying diseased tissue becoming non-functional over time. To avoid this result, the above procedures shift the position of the fovea (i.e., the central portion of the macular portion of the retina which is responsible for a person's sharpest vision) relative to the underlying inner surface of the sclera. This allows the fovea then to be reattached to healthier underlying tissue.
To accomplish this result, the Macular Translocation Procedure, which is less radical than the Retinal Translocation procedure, includes the following steps. First, sutures are placed in a horizontal mattress formation in an arc supero-temporally (i.e., just below the attachment of the recti muscle to the sclera) on the outer surface of the sclera. These sutures typically are located in the same position relative to the eye regardless of the exact location of the diseased tissue. Then, at least the macula portion of the retina is intentionally detached from the underlying tissue. This usually is accomplished by performing a 3 port pars plana vitrectomy followed by the use of a subretinal infusion cannula and a balanced salt solution to create the desired retinal detachment. The pre-placed sutures are then tightened and tied off. This results in the creation of an inwardly extending fold in the sclera that effectively “shortens” the scleral diameter. Thereafter, an air bubble is formed inside the eye so that the excess length of the retina relative to the shortened underlying scleral surface is moved. Then, a partial air-fluid exchange is made. The natural fluid removal generated by the pigment epithelium and choroid allow the macula portion of the retina, which has been shifted relative to the underlying tissue by the deformation of the sclera and by the formation of the air bubble, to settle gradually against, and reattach itself to, healthy tissue. Finally, several days after the surgical procedure, the diseased lesion is treated with standard laser photocoagulation.
The placement of the sutures in the macular translocation procedure is time consuming and, therefore, inefficient. It is also difficult to consistently predict when the retina will settle eventually. In some cases, it may not move at all. It is also difficult to predict the distance of scleral shortening that will result upon the tightening and tie off of the sutures. Further, the skill level required to place and to manipulate the sutures without causing extraneous damage to the eye, or surrounding bodily structures, is high.
Therefore, a need exists to improve the vision in an eye that is suffering from age related macular degeneration and make the surgical results predictable and visible immediately during surgery. There is also a need to move the retina superiorly or inferiorly as desired during the surgery.